Biotic components

5th lecture

Biotic com.Biotic com.

Producers Producers Consumers Consumers Decomposers Decomposers

Producers are able to manufacture their food fromsimple inorganic substances (e.g. CO2). Producers includegreen plants, algae and other photosynthetic protists, andsome bacteria.

Producers

Consumers are organisms that feed on autotrophs oron other heterotrophs to obtain their energy.

•Includes: animals, heterotrophic protists, and somebacteria.

Consumers

Decomposers are consumers that obtain theirnutrients from the breakdown of dead organicmatter.•They include fungi and soil bacteria.

Decomposers

Consumers Consumers

Herbivores Herbivores Carnivores Carnivores Omnivores Omnivores

Living things are classified according

to the way in which they obtain their

energy:

Producers (or autotrophs)

Consumers (or heterotrophs)

Trophic Structure 1

Every ecosystem has a trophicstructure: a hierarchy of feedingrelationships which determines thepathways for energy flow and nutrientcycling.

Species are assigned to trophic levelson the basis of their nutrition.

Producers (P) occupy the first trophiclevel and directly or indirectly supportall other levels. Producers derive theirenergy from the sun in most cases.

Trophic Structure 2All organisms other than producers are consumers(C).

Consumers are ranked according to the trophic level they occupy. First order (or primary) consumers (herbivores), rely directly on producers for their energy.

A special class of consumers, the detritivores, derive their energy from the detritus representing all trophic levels.

Photosynthetic productivity (the amount of food generated per unit time through photosynthesis) sets the limit for the energy budget of an ecosystem.

Consumer(C3)

Consumer(C2)

Consumer(C1)

Producer(P)

Organization of Trophic Levels

Trophic structure can be described by trophic level or consumer level:

Major Trophic Levels

Trophic Level Source of Energy Examples

Producers Solar energyGreen plants, photosynthetic

protists and bacteria

Herbivores ProducersGrasshoppers, water fleas,

antelope, termites

PrimaryCarnivores

HerbivoresWolves, spiders,

some snakes, warblers

SecondaryCarnivores

Primary carnivores Killer whales, tuna, falcons

Omnivores Several trophic levelsHumans, rats, opossums,

bears, racoons, crabs

Detritivores and Decomposers

Wastes and dead bodiesof other organisms

Fungi, many bacteria,earthworms, vultures

Trophic Levels

Organisms can also be identified by the type of food they consume:

Herbivores (Plants) {Deer}

Carnivores (Meat) {Wolves}

Omnivores (Plants/Meat) {Bears}

Scavengers (Carcasses) {Crows}

Detritivores (Debris) {Ants}

Decomposers (All) {Bacteria}

The sequence of organisms, each of which is a source of food for the next, is called a food chain.

Food chains commonly have four links but seldom more than six.

In food chains the arrows go from food to feeder.

Organisms whose food is obtained through the same number of links belong to the same trophic level.

Food Chains

Food chain Food chain

After lion dead

Some consumers (particularly ‘top’ carnivores and

omnivores) may feed at several different trophic levels, and

many herbivores eat many plant species.

For example, moose feed on grasses, birch, aspen, firs, and

aquatic plants.

The different food chains in an ecosystem therefore tend to

form complex webs of feeding interactions called a food

web.

Food Webs

Food Webs

Trophic levels can be compared by determining the number, biomass, or energy content of individuals at each level.

This information can be presented as an ecological pyramid.

The base of each pyramid represents the producers and the subsequent trophic levels are added on top in their ‘feeding sequence’.

Ecological Pyramids 1

Various types of pyramid are used to describedifferent aspects of an ecosystem’s trophicstructure:

Pyramids of numbers: In which the size ofeach tier is proportional to the number ofindividuals present at each trophic level.

Pyramids of biomass: Each tier represents thetotal dry weight of organisms at each trophic level.

Pyramids of energy (production): The size ofeach tier is proportional to the production (e.g. inkJ) of each trophic level.

Ecological Pyramids 2

Pyramid of numbers

No.ofOrganisms

Producers

C1

C2

10

6

1

Pyramid of biomass

Biomass

Producers

C1

C2

20kg

10 kg

5 kg

Pyramid of energy

• In pyramids of biomass, dry weight is usuallyused as the measure of mass because the water content of organisms varies

• Pyramids of energy (or production) are often very similar in appearance to pyramids of biomass.

Thank you